_CALENDERING, CUTTING, AND FINISHING._
Web-glazing.--Glazing Calender.--Damping-Rolls.--Finishing.--
Plate Glazing.--Donkin's Glazing Press.--Mr. Wyatt on American
Super-calendering.--Mr. Arnot on Finishing.--Cutting.--Revolving
Knife Cutter.--Bertrams' Single-sheet Cutter.--Packing the
Finished Paper.--Sizes of Paper.
To impart a higher gloss, or, as it is technically termed "glaze,"
to paper after it leaves the machine, it has to be subjected to
further calendering, which is accomplished either in the web, or in
sheets, according to the quality of the paper.
[Illustration: Fig. 37.]
=Web-Glazing.=--_Glazing Calender._--When paper has to be glazed
in the web, it is passed between a series of rolls, which are
constructed upon several different systems. In one form of this
machine the rolls are alternately of finely polished iron, and
compressed paper, or cotton, the iron rolls being bored hollow to
admit of their being connected to steam pipes, for heating them
when necessary. In this machine there are eight rolls, the centre
pair being both paper rolls, which have an effect equivalent to
reversing the paper, by which both sides are made alike. Another
form of glazing calender, of American origin, but which has
been improved upon by our own engineers, consists of a stack of
rolls made from chilled iron, the surfaces of which are ground
and finished with exquisite precision upon a system adopted in
America. A representation of this calender as manufactured by
Messrs. Bentley and Jackson is given in Fig. 37. Such rolls as
require heating are bored through, and their ends fitted with
brass junctions and cocks, to regulate the admission of steam.
The standards are of cast iron, planed and fitted with phosphor
bronze bearings; the bearings to carry the top roll of the stack
are furnished with wrought-iron screws and hand wheels, and
wrought-iron lifting links can be attached to raise one or more of
the rolls, according to the finish required on the paper. Compound
levers are also supplied, to regulate and adjust the pressure on
the ends of the rolls.
[Illustration: Fig. 38.]
_Damping Rolls._--An important improvement in connection with
the calendering of paper was introduced by Messrs. G. and W.
Bertram a few years since, by which a higher finish is given to
the paper than had previously been attainable. This consists
of a damping apparatus A (Fig. 38) which is placed between the
last drying cylinders B of the machine and the glazing calenders
C. The damping-rolls consist of two brass or copper rolls,
about 14 inches in diameter, through which a constant stream of
cold water is passed, while a line of steam jets, issued from
finely-perforated pipes, plays over the face of the rolls. The cold
water within the rolls condenses the steam, thereby imparting a
uniform moisture to the under surface of the paper, which enables
it to take a better surface when passing through the glazing
rolls. The steam-pipes can be regulated so as to give any amount
of dampness required by adjusting the steam cocks accordingly.
By reference to the engraving, it will be observed from the
disposition of the rolls that the web of paper is reversed, thus
equalising the moisture on both sides, by which the paper-maker is
enabled to produce an evenly-finished paper.
[Illustration: Fig. 39.]
The chilled-iron glazing-rolls, as originally introduced, were
fitted up in stacks of seven, and sometimes as many as nine rolls,
but it was found in practice that so large a number of rolls gave
unsatisfactory results; the heavy pressure, acting on the paper
immediately after leaving the drying cylinders, had the effect of
"crushing" the paper, giving it a thin feel. It is now considered
preferable to use calenders having not more than four, or at most
five rolls. An arrangement of this description, manufactured
by Bertrams, is represented in Fig. 39. The system recommended
by Mr. Dunbar is to employ three sets of rolls, disposed as
follows:--"First, a set of three rolls; second, a set to consist
of four rolls, and a stack of five to give the finishing or dry
surface. With this arrangement of calenders, and the assistance
of the damping apparatus, any desired surface can be got by
varying and regulating the drying of the paper, which any careful
machine-man can do with ordinary attention."
=Finishing.=--To give a still higher finish to the paper, it is
subjected to what is termed "friction-glazing," which consists in
passing it through a stack of rolls, formed alternately of small
iron rolls and larger paper ones, the iron rolls revolving at a
much higher speed than the paper-rolls. The effect of this final
glazing operation gives the paper a very fine surface.
=Plate-Glazing.=--_Donkin's Glazing Press._--This term, which
is also called "super-calendering," is applied to a method of
glazing hand-made paper, and is also adopted for the better
qualities of machine-made paper. It consists in placing sheets of
paper between highly polished plates of either copper or zinc,
the latter being more generally used. The metal plates, with the
sheets of paper placed alternately between them, are made up into
packs or "handfuls" (the operation being usually performed by
women), and these are passed between two powerful rolls, giving a
pressure of from twenty to thirty tons, and each pack, consisting
of about forty plates and as many sheets, is passed through the
rolls several times, the pressure being regulated by means of
screws or levers and weights acting on the ends of the top roll.
A machine for glazing paper in packs, manufactured by Messrs.
Bryan Donkin and Co., is shown in Fig. 40. Some descriptions of
paper, as "antique" and "old style," for example, are surfaced with
good cardboard instead of copper or zinc plates. As soon as the
handful has passed through the rollers, the motion of the machine
is reversed, by which means the pack is made to pass forwards
and backwards repeatedly, according to the extent of gloss or
smoothness required.
[Illustration: Fig. 40.]
=Mr. Wyatt on American Super-calendering.=--Mr. Wyatt, on a
recent visit to America, had many opportunities of witnessing the
systems of manufacture adopted there, and subsequently delivered an
interesting address to the members of the Paper-Makers' Club,[27]
in which he acknowledged the superiority of the high-class printing
papers for book-work, which has so often been the subject of
recognition in this country. Indeed, if we compare the surface of
the paper used even for ordinary technical journals in America
and that generally adopted for our own periodicals of a similar
class, we are constrained to admit that the difference is in
favour of our transatlantic competitors. "In the manufacture of
high-class super-calendered printing papers," Mr. Wyatt observes,
"for fine book-work, or as they call them book papers, the
Americans certainly excel. Whether this be due to the kind of raw
material used, to the almost universal use of the refining-engine,
which renders the pulp very soft and mellow, or to the state of
perfection to which they have brought the art of super-calendering,
or perhaps due to all three, I could not exactly determine. The
material generally used for this class of paper is poplar chemical
fibre and waste paper to the extent of 50 per cent., and even up to
75 and 80 per cent. of the total fibre, the balance being rags, or,
in cheaper qualities, sulphite wood pulp; the stuff is all mixed
together in large beaters, holding from 800 lbs. up to 1,500 lbs.
of pulp, where it is about half beaten, and then finished in one or
other form of refining-engine.
"The Americans have, I think, more thoroughly studied the question
of super-calendering paper than we, and in this respect get better
results and better work. The paper is mostly slit and trimmed
on the paper-machine, and reeled up in from two to four widths
by an ingenious contrivance called the _Manning-winder_, which
automatically keeps the tension constant on each of the reels,
whatever the diameter, and is super-calendered in narrow widths on
small calenders. These calenders are from 36 inches to 42 inches
wide, and consist of a stack of 9 to 11 rolls, alternately chilled
iron, and cotton or paper; the paper is passed through the rolls
two or three times, never less than twice, under great pressure
applied by hand-screws. The power required is very high, being
from 40 to 50 h.p. for each calender, and the speed from 450 feet
up to 600 feet per minute. The paper is not usually damped before
calendering, but is left rather under-dried from the machine;
neither is steam heat used in the rolls, which get very warm,
owing to the high speed at which they run. The rolls are driven
entirely by straps, the arrangements for the fast and slow speed
and for reeling on and off the paper being well designed and
worked out; the main strap, running at high speed, runs on a loose
pulley on the shaft of the bottom roll, by means of a powerful
friction clutch; this pulley can be made a tight one. On this
same bottom shaft is keyed a multiple V-shaped grooved friction
pulley. Another, and independent shaft, driven from the main shaft
by a crossed belt, has a small grooved pulley keyed on it, which
can be thrown in and out of gear with the large grooved pulley.
Strap-driving is thus secured throughout, and the speed can be
increased gradually without jerks, from the starting up to the
fastest speed by working the levers, gearing the friction clutch
and pulleys slowly."
In reference to the high finish of American papers, we are disposed
to attribute this mainly to the nature of the chief raw material
used--wood fibre. In the year 1854, when specimens of Mr. Charles
Watt's wood-fibre paper were first printed upon, the remarkable
gloss of the wood paper attracted much attention, and it was
noticed that the impression of the ink appeared to be well _on the
surface of the paper_, and not, as was often the case with ordinary
printing papers of the time, partially absorbed by the paper
itself. Mr. Wyatt states that poplar chemical fibre and waste paper
to the extent of 50 per cent., and even up to 75 and 80 per cent.,
are used, the balance being rags; now since the waste paper in all
probability would be composed largely of wood fibre, and as, in the
cheaper qualities, sulphite wood pulp is used in lieu of rags, it
will be fair to assume that the chief basis of the highly-finished
papers for which the Americans are justly famous is wood fibre, and
we believe that there is no other variety of cellulose which is so
susceptible of producing a naturally glossy paper as that which is
obtained from wood by the soda process.
=Mr. Arnot on Finishing.=--Mr. Arnot makes the following
observations respecting the finishing of paper:--"The paper may
be slit into widths, suitable for wet calenders, or may be cut up
into sheets, and glazed by the plate or board calenders. The former
method of surfacing or finishing has come extensively into use
in recent times, the labour involved being much less than in the
older method of finishing in sheets. Still, however, the plate
calenders are kept at work upon the higher classes of goods, it
being possible to give almost any degree of surface to good paper
by that means. There is little doubt, too, that the paper glazed by
the plate rolls retains its original softness to a greater degree
than that passed through web calenders. In the latter it is exposed
in one thickness to great pressure, and is thinned in consequence;
whereas, when the sheets are made up into piles, along with copper
or zinc plates, there is a certain amount of spring or elasticity
in the treatment which largely counteracts the crushing action of
the rolls. The web calenders consist of a series of rollers erected
in a vertical frame, and between these the paper winds, beginning
at the top and coming downwards, so that the pressure gradually
increases as the paper moves on its journey. It will be observed
that the under rolls have to bear the weight of the upper ones,
and that consequently the pressure on the paper will be greater
the lower down it descends. Many of the rollers themselves are now
made of paper, and as these possess a slight degree of elasticity,
and take a high polish, they are alternated with iron rollers
with good effect. The paper-rolls are made by sliding an immense
number of circular sheets, perforated in the centre, on to an iron
core or shaft, pressing these close together by hydraulic action,
and trimming them off on the lathe. The plate or broad calenders
consist only of two rollers, the upper one heavily weighted,
preferably by compound levers. Between these rollers the sheets
of paper, alternated with plates of copper or zinc, and made up
into bundles about an inch in thickness, are passed backwards and
forwards, the reciprocating action being produced by the movement
of a lever in the hand of an attendant. The metal and paper sheets
of different bundles may be interchanged, and the process repeated
with the effect of increasing the beauty and equality of the
finish."
[Illustration: Fig. 41.]
=Cutting.=--_Revolving Knife._--When paper is to be used in a
continuous printing-machine, or, as is often the case, has to
be exported in the web, it is supplied in rolls; otherwise it
is cut into sheets before leaving the mill. The form of cutter
generally used is what is termed the _revolving knife-cutter_, an
illustration of which, as manufactured by Bertrams, Limited, is
shown in Fig. 41. At A is shown a series of webs, the paper from
which is drawn forward by the rolls, B, and is then slit into
suitable widths, and the margin at the same time pared by circular
knives, one of which is shown at C. It then passes through a pair
of leading-rolls, after which it comes in contact with a knife,
D, attached to a revolving drum, E, pressing against a dead knife
not shown in the engraving. The sheets, as they are thus cut, drop
upon a travelling felt or apron, F, from which they are lifted and
placed in piles, by boys or girls standing on each side of the
felt. These machines will cut eight webs at one time.
[Illustration: Fig. 42.]
_Bertrams' Single-sheet Cutter._--In cases where it is necessary
that the sheets should be cut with great uniformity, as in the
case of paper bearing a water-mark, in which it is requisite that
the design should appear exactly in the centre of the sheet,
the ordinary cutter is not found to be sufficiently reliable; a
machine termed a "single-sheet cutter" is therefore used for this
purpose, of which an illustration is shown in Fig. 42. The paper
is led direct from the paper-machine, or from a reel frame, to the
drawing-in rolls, A; after which it passes through the circular
slitting-knives, B; from here it is led by the roller C to a large
wood-covered drum, D, and at the front of this drum the sheets are
cut by the cross-cutting knives, E. There are two cast-iron tapered
cones, with belt guide for adjusting the speed; a fly-wheel to
promote steadiness in working; a series of wrought-iron levers,
cranks, eccentrics, shafts, etc., for accurately regulating the
travel of paper and the cut of the horizontal knives; a small
pasting table is also fitted across the machine for mending broken
sheets.
=Packing the Finished Paper.=--The paper, after it leaves the
cutting-machine, is conveyed to the _finishing-house_, where it
is carefully examined by women, who cast aside all defective or
damaged sheets, which, under the trade names of "imperfections"
or "retree," are sometimes disposed of, at a lower rate, to the
customer for whom the order is executed. In the warehouse these
imperfections are marked with a capital R on the wrapper, or two
crosses, thus =X X=. If the paper is broken, it is sometimes
marked B =X X=; it is not generally the custom, however, to
sell imperfections, but to return them to the beater-man, to be
re-converted into pulp. The perfect sheets are then counted, and
packed up in reams consisting of 480 to 516 sheets.
=Sizes of Paper.=--The various sizes of paper are known in the
stationery trade under different designations, as demy, crown,
double crown, royal, imperial, etc. As paper is generally purchased
according to weight, the various weights per ream are also
distinguished with the size of the paper, as 16 lb. demy, 22 lb.
double crown, and so on. The following table shows the sizes of
some of the writing and printing papers in common use:--
+----------------------+----------------+-----------------+
| Name. | Writing | Printing |
| | Papers. | Papers. |
+----------------------+----------------+-----------------+
| | Inches. | Inches. |
| Foolscap | 17 × 13¼ | 17 × 13¼ |
| Small post (or post) | 18¾ × 15¼ | 18¾ × 15¼ |
| Crown | | 20 × 15 |
| Double crown | | 30 × 20 |
| Demy | | 22½ × 17¾ |
| Royal | | 25 × 20 |
| Imperial | | 30 × 22 |
| Double demy | | 35½ × 22½ |
| Double royal | | 40 × 25 |
+----------------------+----------------+-----------------+